In the manufacturing of semiconductor devices, etc., used in electronics technologies leading information society, silicon wafers may not be omitted. Characteristics of silicon wafers include micro defects such as oxygen precipitate, dislocation, oxygen stacking faults and the like. Micro defects are advantageous for capturing heavy metal pollution that occurs in a device process, but may become a source of device failure. Therefore, there may be a need to adjust the oxygen concentration in a crystal to a predetermined concentration corresponding to types of devices or device processes used.
As a current method of manufacturing silicon single crystals, the “Czochralski method” (hereinafter referred to as “CZ method”) of manufacturing silicon single crystals through pulling is generally used. In addition, there is a method called the magnetic field applied Czochralski method (MCZ method) which is a CZ method performed under a strong magnetic field.
In the CZ method, a polycrystal silicon that is highly purified with a metal impurity concentration of a few ppb (parts-per-billion, 1 ppb=10−9) or less is generally put into a high-purity vitreous silica crucible together with a resistivity control dopant (e.g., boron (B) or phosphorous (P)) and is melted at a temperature of about 1,420 deg. C. Continuously, a seed crystal silicon rod is brought into contact with a surface of silicon melt, the seed crystal or the vitreous silica crucible is rotated to make the seed crystal thin (dislocation-free) and then the seed crystal is pulled up, thereby enabling a silicon single crystal ingot having the same atomic structure as the seed crystal to be obtained.
As aforementioned, the vitreous silica crucible is a container to put silicon melt therein when pulling molten polycrystalline silicon into a single crystal. Vitreous silica is progressively molten into the silicon melt. For this reason, the vitreous silica crucible, as described above, serves as an oxygen source supplying oxygen to a silicon wafer when pulling the single crystal, and also serves as an impurity source supplying trace impurities such as Fe, Al and Na. Furthermore, defects contained in the vitreous silica(silica glass) are also melted and mixed into the silicon melt. Representative defects include bubbles with φ0.05 mm or more in diameter and metal pieces such as iron pieces.
During the pulling of single crystal silicon by CZ method, if bubbles with φ0.05 mm or more in diameter are exposed or burst, broken small pieces of vitreous silica drop into the silicon melt. The pieces of vitreous silica move by the heat convection of the silicon melt, and adhere to a silicon single crystal. This causes silicon single crystal to be polycrystallized, thereby resulting in a decrease in yield of single crystal. Moreover, gases in the bubble are also mixed into the silicon melt. In the case where these gases are introduced into a silicon single crystal, they become defects of the silicon single crystal. Impurities such as iron which are contained in the vitreous silica cause O—Si—O bonds of the vitreous silica to be broken and transferred to a stable crystal (β-cristobalite) at a single crystal growing temperature, and thus a peripheral region around the metal pieces are crystallized. Since this crystal is peeled off when exposed to the silicon melt, it is mixed into the silicon melt like bubbles, leading to a decrease in yield of single crystal. Recently, accompanied with the tendency for implementing crucibles having large diameter (700 mm or more), a single crystal growing temperature becomes higher in the case of performing CZ method using a vitreous silica crucible, and therefore vitreous silica tends to be melted faster than before. Also, the manufacturing time of single crystal by CZ method is made longer to thereby increase the molten amount of vitreous silica, and thus the above-described problems becomes more serious.
Although having absolutely different objectives from that of the present invention, a related art technology of providing a mark at a vitreous silica crucible, for example, a technology of installing a detachable_mark member to the crucible is disclosed in Patent Document 1 below.